Solid-State Divalent Ion Conduction in ZnPS_3

Next-generation batteries based on divalent working ions have the potential to both reduce the cost of energy storage devices and increase performance. Examples of promising divalent systems include those based on Mg^(2+), Ca^(2+), and Zn^(2+) working ions. Development of such technologies is slow, however, in part due to the difficulty associated with divalent cation conduction in the solid state. Divalent ion conduction is especially challenging in insulating materials that would be useful as solid-state electrolytes or protecting layers on the surfaces of metal anodes. Furthermore, there are no reports of divalent cation conduction in insulating, inorganic materials at reasonable temperatures, prohibiting the development of structure–property relationships. Here, we report Zn^(2+) conduction in insulating ZnPS_3, demonstrating divalent ionic conductivity in an ordered, inorganic lattice near room temperature. Importantly, the activation energy associated with the bulk conductivity is low, 351 ± 99 meV, comparable to some Li+conductors such as LTTO, although not as low as the superionic Li+ conductors. First-principles calculations suggest that the barrier corresponds to vacancy-mediated diffusion. Assessment of the structural distortions observed along the ion diffusion pathways suggests that an increase in the P–P–S bond angle in the [P_2S_6]^(4–) moiety accommodates the Zn^(2+) as it passes through the high-energy intermediate coordination environments. ZnPS_3 now represents a baseline material family to begin developing the structure–property relationships that control divalent ion diffusion and conduction in insulating solid-state hosts

Understanding the role of crystallographic shear on the electrochemical behavior of niobium oxyfluorides

The effects of shear planes in perovskite materials have been studied in order to identify their role in the electrochemical behavior of Li⁺ intercalation hosts. These planes modulate the structural stability and ionic transport pathways and therefore play an intimate role in the characteristics and performance of shear compounds. Herein, two Nb-based compounds, NbO₂F and Nb₃O₇F, were chosen as representative perovskite and shear derivatives respectively to investigate the role of crystallographic shear. A series of operando measurements, including X-ray diffraction and X-ray absorption spectroscopy, in conjunction with structural analysis, Raman spectroscopy, and detailed electrochemical studies identified the effect of shear planes. It was found that shear planes led to increased structural stability during Li⁺ (de)intercalation with shear layers being maintained, while perovskite layers were seen to degrade rapidly. However, disordering in the shear plane stacking introduced during delithiation ultimately led to poor capacity retention despite structural maintenance as Li⁺ diffusion channels are disrupted

Solid-State Divalent Ion Conduction in ZnPS_3

Next-generation batteries based on divalent working ions have the potential to both reduce the cost of energy storage devices and increase performance. Examples of promising divalent systems include those based on Mg^(2+), Ca^(2+), and Zn^(2+) working ions. Development of such technologies is slow, however, in part due to the difficulty associated with divalent cation conduction in the solid state. Divalent ion conduction is especially challenging in insulating materials that would be useful as solid-state electrolytes or protecting layers on the surfaces of metal anodes. Furthermore, there are no reports of divalent cation conduction in insulating, inorganic materials at reasonable temperatures, prohibiting the development of structure–property relationships. Here, we report Zn^(2+) conduction in insulating ZnPS_3, demonstrating divalent ionic conductivity in an ordered, inorganic lattice near room temperature. Importantly, the activation energy associated with the bulk conductivity is low, 351 ± 99 meV, comparable to some Li+conductors such as LTTO, although not as low as the superionic Li+ conductors. First-principles calculations suggest that the barrier corresponds to vacancy-mediated diffusion. Assessment of the structural distortions observed along the ion diffusion pathways suggests that an increase in the P–P–S bond angle in the [P_2S_6]^(4–) moiety accommodates the Zn^(2+) as it passes through the high-energy intermediate coordination environments. ZnPS_3 now represents a baseline material family to begin developing the structure–property relationships that control divalent ion diffusion and conduction in insulating solid-state hosts